1. Field of the Invention
The present invention relates to a magneto-optical recording medium for reproducing a signal by enlarging a magnetic domain by moving domain walls, and more particularly to a technique for canceling a ghost signal.
2. Description of the Related Art
In recent years, a magneto-optical reproducing method has been suggested which employs a triple-layered magnetic film consisting of a displacement layer, a switch layer and a memory layer. Thus, movement of domain walls of the displacement layer takes place when the temperature of the film has been raised to a level not lower than the Curie temperature is used. This effectively enlarges the size of the recording magnetic domain so as to intensify a reproduction carrier signal.
The foregoing method called, xe2x80x9cDWDD (Domain Wall Displacement Detection)xe2x80x9d, is able to reproduce an intense signal even from a fine recording magnetic domain, the period of which is not longer than the optical limit of separative power of reproduction light. Therefore, the foregoing method is one of advantageous methods which is capable of raising the density without a necessity of changing the wavelength of light and the numerical aperture NA of an objective lens.
The DWDD, however, suffers from a multiplicity of problems which must be overcome. For example, behavior is displayed such that when a signal having a period longer than a certain period is reproduced, a signal corresponding to the recording magnetic domain of the signal appears. Then, the signal disappears temporarily, and then the signal again appears.
The foregoing phenomenon is called xe2x80x9cghostxe2x80x9d. It is difficult to determine whether the signal allowed to appear is the ghost signal or the signal corresponding to a next recording magnetic domain. Moreover, there arises a problem in that the noise-level is raised in the vicinity of the period of the recording magnetic domain in which appearance of the ghost signal starts. As a result, there arises a problem in that the recording density cannot satisfactorily be raised.
An object of the present invention is to prevent a ghost phenomenon experienced with a DWDD magneto-optical recording medium.
The inventors of the present invention have performed a variety of studies to achieve the above-mentioned object. A magneto-optical recording medium according to the present invention has been found in accordance with results of the studies. The principle lies in preventing unnecessary movement of domain walls of the displacement layer.
The magneto-optical recording medium according to the present invention comprises: a recording layer constituted by a multi-layered magnetic film composed of at least three magnetic layers, wherein domain walls of the magnetic layer adjacent to the portion irradiated with reproducing light are moved toward the center of the spot in a forward portion in a direction, in which the reproducing light spot is moved, so that a recording magnetic domain is enlarged, and movement of the domain walls of the magnetic layer adjacent to the portion irradiated with reproducing light is inhibited in a rear portion in the direction in which the reproducing light spot is moved.
The movement of the domain walls of the magnetic layer adjacent to the portion irradiated with the reproducing light is inhibited in the rear portion in the direction in which the reproducing light spot is moved. Thus, the ghost phenomenon can be prevented.
To inhibit the movement of the domain walls of the magnetic layer adjacent to the portion irradiated with reproducing light, for example, insertion of a magnetic layer having a predetermined magnetic characteristic between the displacement layer and the switch layer is required. As a result, a ghost can be prevented while the characteristics of the DVDD are being maintained.